The method for producing a conducting organic polymer containing an electrolytic ion as a dopant, and having electric conductivity of more than 10.sup.-6 S/cm by chemical oxidative polymerization of aniline with a chemical oxidizing agent is already known (U.S. Pat. No. 4,615,829), and further, the fact that, in the production of a conducting organic polymer by use of such chemical oxidative polymerization, an oxidizing agent having the standard electrode potential determined as an electromotive force in the reduction half cell reaction making the standard hydrogen electrode as a standard of more than 0.6 V is used preferably, is also already described in the official publication of Japanese Patent Application Laid-Open No. 258831/1986.
However, since the conducting organic polymer is generally insoluble and infusible, it cannot be formed into a film, and hence, there is a large hindrance for developing useful applications of the conducting organic polymer. As described in the official publication of Japanese Patent Application Laid-Open No. 235831/1985 and J. Polymer Sci., Polymer Chem. Ed., 26, 1531 (1988), although a film of the conducting organic polymer can be formed on the electrode, since the film formation surface is limitted to the surface of the electrode, it is difficult to obtain a film of large area, and moreover, since the film formation is effected by electrolytic oxidation, the production cost is high. Moreover, this film has low strength and is insoluble and infusible.
Therefore, various conversion methods have been proposed, in which an intermediate product soluble in an organic solvent is to be produced, and after making the solution into a film by the casting method, the intermediate product is changed to a conducting polymer by physical or chemical means. However, according to this method, treatment at a high temperature is required, and the change from the intermediate product to a conducting polymer does not necessarily proceed as shown theoretically, so that the method is not practical also as the production method of the conducting organic polymer film, when seen from the production side and the side of the physical properties of the film obtained.
In the field of polypyrrole or polythiophene, a polymer soluble in an organic solvent is known. The thiophene having a long chain alkyl group as a substitutent and the pyrrole having the alkane sulphonic acid group as a substituent were subjected to electrochemical oxidative polymerisation to obtain respectively poly-3-alkyl thiophene soluble in an organic solvent and poly-pyrrole-alkane sulphonic acid soluble in water. Films of any of these polymers can be obtained from their solutions by the casting method. However, this method uses special monomers in either case, and in addition, it must be subjected to electrochemical oxidative polymerisation, so that the production cost is extremely high.
On the other hand, in the field of chemical oxidative polymerisation of aniline, it is reported, in recent years, that a polyaniline soluble in an organic solvent can be obtained by applying about 1/4 amount of ammonium peroxodisulpate as an oxidizing agent to aniline, to let aniline be subjected to chemical oxidative polymerization. (A. G. MacDiarmid et al., Synthetic Metals, 21, 21 (1987); A. G. MacDiarmid et al., L. Alcacer (ed.), Conducting Polymers, 105-120, D. Reidel Publishing Co., 1987)). However, this polymer is soluble not only in N-methyl-2-pyrrolidone and dimethyl sulphoxide, but also, in 80% acetic acid and 60% formic acid aqueous solution, and its molecular weight is low. It is also described that a free-standing film can be obtained from the solutions of the polymer in N-methyl-2-pyrrolidone and dimethyl sulphoxide. Further, it is also described that a conducting polymer film doped with acetic acid can be obtained from an acetic acid solution, and this is made as a film undoped with ammonia. However, since the film in this undoped state has a low molecular weight of polyaniline, its strength is low, and it is easily broken by bending, and it is hardly suitable for practical use.
Also, it is known that polyaniline soluble in tetrahydrofuran can be obtained by oxidising aniline with ammonium peroxodisulphate (J. Tang et al., Synthetic Metals, 24, 231 (1988)). However, this polymer can be considered to have a low molecular weight, since it dissolves in tetrahydrofuran.